Specificity of experience-dependent pitch representation in the brainstem.
ABSTRACT Crosslanguage comparisons of brainstem-evoked potentials have revealed experience-dependent plasticity in pitch representation for curvilinear f0 contours representative of Mandarin tones. To assess the tolerance limits of this experience-dependent selectivity, we evaluated cross-linguistically (Chinese, English) the pitch strength and tracking accuracy of linear rising and falling f0 ramps representative of Mandarin tones 2 and 4. No crosslanguage differences in pitch strength or accuracy were observed for either tone, indicating that stimuli with linear rising/falling ramps elicit homogeneous pitch representations at the level of the brainstem regardless of language experience. We conclude that pitch extraction at the brainstem level is critically dependent on specific dimensions of pitch contours that native speakers have been exposed to in natural speech contexts.
Full-textDOI: · Available from: Ananthanarayan Krishnan, Jun 08, 2015
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Article: Specificity of experience-dependent pitch representation in the brainstem.
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ABSTRACT: Pitch is a robust perceptual attribute that plays an important role in speech, language, and music. As such, it provides an analytic window to evaluate how neural activity relevant to pitch undergo transformation from early sensory to later cognitive stages of processing in a well coordinated hierarchical network that is subject to experience-dependent plasticity. We review recent evidence of language experience-dependent effects in pitch processing based on comparisons of native vs. nonnative speakers of a tonal language from electrophysiological recordings in the auditory brainstem and auditory cortex. We present evidence that shows enhanced representation of linguistically-relevant pitch dimensions or features at both the brainstem and cortical levels with a stimulus-dependent preferential activation of the right hemisphere in native speakers of a tone language. We argue that neural representation of pitch-relevant information in the brainstem and early sensory level processing in the auditory cortex is shaped by the perceptual salience of domain-specific features. While both stages of processing are shaped by language experience, neural representations are transformed and fundamentally different at each biological level of abstraction. The representation of pitch relevant information in the brainstem is more fine-grained spectrotemporally as it reflects sustained neural phase-locking to pitch relevant periodicities contained in the stimulus. In contrast, the cortical pitch relevant neural activity reflects primarily a series of transient temporal neural events synchronized to certain temporal attributes of the pitch contour. We argue that experience-dependent enhancement of pitch representation for Chinese listeners most likely reflects an interaction between higher-level cognitive processes and early sensory-level processing to improve representations of behaviorally-relevant features that contribute optimally to perception. It is our view that long-term experience shapes this adaptive process wherein the top-down connections provide selective gating of inputs to both cortical and subcortical structures to enhance neural responses to specific behaviorally-relevant attributes of the stimulus. A theoretical framework for a neural network is proposed involving coordination between local, feedforward, and feedback components that can account for experience-dependent enhancement of pitch representations at multiple levels of the auditory pathway. The ability to record brainstem and cortical pitch relevant responses concurrently may provide a new window to evaluate the online interplay between feedback, feedforward, and local intrinsic components in the hierarchical processing of pitch relevant information.Acoustics Australia / Australian Acoustical Society 12/2014; 42(3):166-178. · 0.36 Impact Factor
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ABSTRACT: To perceive and produce Mandarin, adult second language (L2) learners need to learn to discriminate lexical pitch variations and develop the new sensorimotor skills needed to produce the lexical tones. In this paper, we investigated whether auditory discrimination and sensorimotor integration differ with Mandarin (tonal) language experience in the context of tonal language syllables and simple sustained vowels. We tested four distinct groups: native Mandarin speakers, Mandarin L2 adults, trained vocalists, and naïve adults (those with no tonal language exposure). Auditory discrimination was measured using two perceptual tasks, musical tone discrimination and Mandarin tone discrimination, the results of which were compared across the four groups. Group differences in sensorimotor integration related to lexical tone production were examined with a pitch-shift paradigm that assessed rapid motor responses to unexpected pitch perturbations. Mandarin speakers performed significantly better on Mandarin tone discrimination compared to the other three groups. Mandarin speakers also showed more attenuation of pitch-shift response amplitude (better vocal pitch control) during production of both the sustained vowel and Mandarin tones, especially compared to naïve speakers. These findings suggest that Mandarin speakers have more robust pitch control over self-produced vocalizations and are thus less affected by auditory feedback perturbations. This effect was particularly evident in response to the Mandarin high level lexical tone, for which the pitch-shift compensation patterns (with apparent attenuation in Mandarin speakers only) differed qualitatively from those of sustained vowels (with clear compensation in all groups), the rising tone (with apparent attenuation in all groups but naïve speakers), and the falling tone (with apparent attenuation in all groups). Trained vocalists also appear to rely more than naïve speakers on internal models when regulating voice F0 in the nonlinguistic domain (sustained vowel), but not in the linguistic domain (Mandarin tone). Native Mandarin speakers demonstrate robust internal models for lexical tone in both perception and production; this underscores the importance of developmental language experience but also provides evidence for the declination of the high level lexical tone which requires a mastery of tonal languages.Journal of Phonetics 01/2015; DOI:10.1016/j.wocn.2014.12.003 · 1.41 Impact Factor
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ABSTRACT: Tonal languages provide a window for tracing the hierarchical transformation of the pitch of a sound from early sensory to later cognitive stages of processing in the human brain. Hemispheric laterality of pitch is driven by multiple dichotomies or scalar features that apply during real-time intervals at cortical and subcortical levels. Using functional neuroimaging, we show that pitch processing recruits the hemispheres differentially as a function of its phonological relevance to the listener. Mismatch negativity, a neural index of early, cortical processing, shows that pitch processing is shaped by the relative saliency of tonal features. Frequency following response, a neural index of brainstem pitch encoding, shows that enhancement of pitch features is sensitive to rapidly-changing segments of tonal contours, and that ear asymmetries can be modulated by functional changes in pitch based on linguistic status. We conclude that nascent representations of acoustic-phonetic features emerge early along the auditory pathway.